Electronic conductivity meter



Jan.

Filed Set. 29 1948 INVENTOR.

/fl/RT ALBRECHT Patented Jan. 12, 1954 UNITED STATES RATENT ELECTRONIC CONDUCTIVITY METER Application September 29, 1948, Serial No. 51,662

2 Claims.

Wheatstone bridge and the direction of unbalance as well.

An object of this invention is to provide an electronic conductivity meter of the character referred to above that shall be extremely simple insofar as the circuit is concerned, operable from the ordinary 110 volt alternating current service outlets without the use of high voltage transformers in any of its circuits and branches and arranged to give visual balance, and directional indication of unbalance.

A further object of the invention is to provide a conductivity meter of the type referred to above, in which the balance point of the bridge is sharply and accurately defined by the cathode ray discharge tube, and the direction of unbalance, when unbalance occurs, thereby enabling one to make accurate measurements of conductivity of solutions, the resistance value of unknown resistances, or the use of resistance thermometers in the bridge at the point where the unknown resistance or conductivity will be determined, all as will be apparent to those skilled in this art from the following specifications and drawings hereto annexed.

These and other objects are attained by the conductivity meter embodying the invention described in the following specification and illustrated in the accompanying drawings, in which: Figure 1 is a diagrammatic illustration of an electronic conductivity meter arranged and constructed in accordance with what now appears to be a preferred form of the invention; and

Figure 2 is a group view illustrating the balance point of the cathode ray discharge tube and the shadow which develops when the Wheatstone bridge is unbalanced in either direction from the balance point.

Throughout the specification and drawings like reference characters indicate like reference parts.

In Figure 1 is illustrated a vacuum tube I!) which provides two independently controlled plate circuits. It is preferred that tube It be a high a twintriode. It is to be understood that two tubes, each having a single plate, could also be employed but the twin triode is preferred. Tube IIJ may be of a type known as the R. C. A. 6807. This tube includes plates or anodes II and I2, a cathode heater I3, an indirectly heated cathode I4 and control grids I5 and I6 associated with plates II and I2, respectively. The meter includes also a cathode ray discharge tube I! of the type known as the R. C. A. BAFSG tube. This tube includes a plate or target I8, which, when bombarded, gives off a fluorescent green color, all as is well known to those skilled in this art. The tube is provided with a plurality of control electrodes I9 and 26, an indirectly heated cathode 22, and a cathode heater 2i. The target or anode I8 of tube i? is connected to the plate side of the circuits for plates I I and I2 containing resistors 23 and 2 s, and the indirectly heated cathodes is: and 22 are connected to input conductor 25. The common connection of the target I8 and the plates I I and 92 through resistors 23 and 2 3 is connected to an input conductor 2'1. Input conductors 2t and 2? may be plugged into any service receptacle having volt commercial frequency alternating current. Control electrode 20 of tube I 'I is connected to the plate circuit ll between resistor 24 and plate II, and the control electrode I9 is connected to the plate circuit I2 between resistor 23 and plate I2. It will be apparent that electrode I9 can also be connected to resistor 23 at such a point between the ends thereof as will provide the necessary drop in potential to aiTect a change in the potential of electrode It with respect to the potential of electrode 26.

When control grid I5 is more positive than control grid It more current flows through resistor 25 and plate I I to the cathode It than through resistor 23 and plate I2 to cathode It, causing the voltage or potential at the point where control grid 20 is connected in the circuit of plate II, to change with respect to the potential on control grid I9. This change causes electrons to be deflected to one side of target I8 and produce a shadow such as shown at A in Figure 2. When more current flows through the circuit of plate I2, than through the circuit of plate H, control grid l6 being more positive than control grid I5, the potential on control grid It is changed with respect to the potential on grid 20. This change causes deflection of electrons to the other side of target I8, thereby producing a shadow such as shown at C in Figure 2. When both control grids i5 and it are at the same potential and the same amount of current flows through the plate circuits of plates 5 i and I2 and is determined by bias resistor 25 then target I3 of tube I1 is free of shadow as the electrons striking it are uniformly distributed, there being only a narrow slit or mark extending diametrically across it as indicated by the line 29 in part B of Figure 2. The current 3 in the plate circuits of plates II and I2 may be adjusted to equal values at the null point of bridge 3| by adjusting bias resistor to proper value or selecting a resistor having such value.

A Wheatstone bridge 3| is provided to control tubes l0 and i1 and is operated on alternating current. Tube H indicates when the bridge is in balance, when it is out of balance, and the direction of unbalance. The input voltage therefor is derived from a transformer 33 having a primary winding connected to the input conductors 26 and 27, and a secondary winding 34 which reduces the voltage to a value much lower than the voltage impressed on the input conductors 26 and 21. I have found that a voltage of 6 volts is sufiicient for input to the Wheatstone bridge but a higher voltage of 30 to 40 volts gives better sensitivity. Transformer 33 is also provided with a low voltage winding 35 for supplying heating current to the cathode heaters i3 and 2! of tubes I0 and H.

The Wheatstone bridge comprises a plurality of resistors 35, 37 and 38 which are connected in series and form two legs or branches of the bridge, a plurality of resistors 30 and 40 connected in series which form a third leg of the bridge, and a dip cell t! which forms the fourth leg of the bridge. Resistor 40 may be a variable resistor provided with a slider 42 or equivalent, by means of which the bridge may be adjusted to compensate for deviation in temperature of the solution in which dip cell 4i is immersed from a reference or standard temperature. Bridge resistor 3! and a slide wire contactor as provide a means for balancing the bridge against the conductivity of the solution to be determined.

The transformer winding 34 is connected to the input terminals of the bridge formed by the junction of resistors 38 and 40 and resistor 3'3 and the connection leading to one terminal of the dip cell. The output or balance points of the bridge 44 and 45 (the point 45 being determined by the point of contact of the slider contact 43 with resistor 37) are connected to the primary winding 41 "of transformer 32. The secondary or output winding 48 of this transformer has its opposite terminals 49 and 50 connected to control grids l5 and [6 respectively, of tube It. Winding 48 is provided with a mid-point tap 52 which is connected to input conductor 28 whereby the indirectly heated cathodes l4 and 22 of tubes l0 and H are connected to the mid-point of winding 48. As shown, a condenser 54 may be connected across the control grids i5 and it. This condenser serves the purpose of a stabilizing condenser.

If it be assumed that the dip cell 45 is immersed in a solution of known conductivity, or that a resistor of known ohmic value is substituted therefor and the bridge balanced, the potential difference across the output terminals 44 and 45 of the bridge will be zero and no current will flow through winding 47 of transformer 32. Under such conditions the same current flows in both of the plate circuits, including plates H and 12 of tube 50. Therefore, since the same current is flowing through both of the plates II and I2, the potential on the control grids l9 and 20 of tube [-1 will be so sufficiently alike that the target 18 will receive uniform distribution of electrons and no shadows corresponding to either portions A or C of Figure 2 will appear. Instead, a thin, narrow line only will be visible on the tube as indicated at B. This is the balance point of the bridge. If the slider 42 of resistor 40 is adjusted to either increase or decrease the resistance of the leg of the Wheatstone bridge in which resistors 39 and 40 are included, then the potential at point 44 will either be higher or lower than it is at point 45, so that either control grid E5 or it will be rendered positive and cause its associated plate circuit to pass more current. If more current is passed by plate I2, then, as explained previously, the potential of control grid i9 is changed and a shadow appears as shown in part C of Figure 2, whereas, if control grid I5 is rendered relatively more positive than control grid it, more current will flow in the plate circuit including plate 1|, whereby the control potential on grid 20 is changed and a shadow appears on target i8 corresponding to that indicated by part A of Figure 2.

As may be observed by inspection of Figure 1, the voltage impressed on plates II and I2 and target If! are always in phase with each other, whereas the potentials impressed on control grids I5 and 16 are always out of phase. Thus when control grid i5 is positive, a current flow in transformer winding 41 being assumed, control grid [6 is negative, and vice versa. The unbalance of the Wheatstone bridge caused by an unknown resistance in the dip cell 4! operates to change the phase of the voltages impressed on the control grids l5 and it, in accordance with the direction of unbalance of the bridge. Thus, if the potential at point 44 of the bridge is higher than it is at point 45, current will flow from point i -i through transformer winding 41 to point 45 of the bridge. In this case control grid 16 would be negative and control grid I5 positive, so that current would flow in the circuit, which includes plate H. When the potential at point 45 is higher than at point 44 the phase relations in the transformer 32 are reversed and the current will flow through winding 41 from point 45 through winding 4! to point 44. In this case, control grid it becomes positive, and control grid i5 negative, so that current flows in the circuit of plate 12. By adjusting the position of slider '42 associated with resistor 40 in the direction indicated by the directional unbalance shown by target K8, the bridge may be restored to balance, the balance being indicated by the narrow slit indicated in part B of Fig. 2.

A dial (not shown) but customarily employed with adjustable resistors may be operatively connected with slide contact 43 and calibrated against known values of resistance in the dip cell arm of the bridge. This calibration may be in ohms or in reciprocal ohms, often termed micromhos, providing a direct reading for each position of the slider contact 43 of the value of the unknown resistance of the dip cell branch.

While the ohmic resistance value of resistors 23, 24, and .25 may vary with the design of the circuit, as may also the ohmic resistance value of the resistors comprising the Wheatstone bridge, I have found that the following values for resistance provide a sensitive and accurately oper-' ating conductivity meter for measuring conductivities of solutions in which dip cell 4| is im-. mersed varying over a range of approximately 500 to 7000 micromhos when the cell has a constant of 2: Y

Resistors 23 and 24 megohm Resistor 25 3500 ohms Variable resistor 36 0 to 600 ohms Variable resistor 31 2000 ohms Variable resistor 40 0 to 750 ohms Resistors 38 and 39 500 ohms each I have found also that a transformer 33 which provides 40 volts output on its secondary winding 34, a sufficient operating voltage for the bridge, and has a winding 35 which produces the voltage for which the heaters for the indirectly heated cathodes l3 and 2| are designed, is satisfactory. This voltage is usually about 6 volts. I have also found that a condenser 54 having a capacity of 0.1 micro-farad is sufiicient for its functional purpose.

If it is necessary or desirable, resistor 36 may be made adjustable by means of a slide wire contact 55, the purpose of which is to adjust the Wheatstone bridge to compensate in part for variations in the characteristics of the dip cell employed.

While I have shown a transformer coupling between the control grids I5 and I6 of tube It) and the output terminals of bridge 3| it will be apparent to those skilled in this art that a resistance coupling may be employed. In such a coupling a resistor would be connected to the output terminals of the bridge, the mid-potential or neutral point thereof would be connected to line 26 like the mid-tap 52 of winding 48 is connected, and grids l5 and It would be connected to the resistor at opposite sides of the mid-point thereof.

The conductivity meter such as shown and described, is particularly useful in the measurement of conductivity of solutions such as boiler waters containing dissolved solids, the conductivity thereof being a measure of the concentration of such solids. Obviously, the meter may be used to measure the conductivity of other solutions. Also, it will be apparent to those skilled in this art that in place of the dip cell 4| a resistance thermometer may be substituted therefor, and the device employed to measure temperature. Other uses will be apparent to those skilled in this particular art without further particularization.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent is:

1. A circuit for controlling the selective energization of diametrically opposite portions of the target in a cathode ray tube, having a control electrode for each portion of the target and a heated cathode, comprising a high ,LL twin triode tube, a resistor connected to each plate of the triode tube, the opposite side of each of said resistors being connected together and being adapted for connection to the same side of an alternating current voltage supply source, said twin triode tube having a cathode and a heater therefor, and a control grid for each plate, said cathode being connected to one side of a resistor of relatively high ohmic value, the other side of said resistor being adapted for connection to the other side of said voltage supply, the cathode ray tube having its target connected to the supply voltage side of the plate resistors of the twin triode tube, and its control electrodes connected respectively to the plate sides of said triode plate resistors, the heated cathode of said cathode ray tube being connected to the voltage supply side of the heated cathode of the triode tube, the control grids of said triode tube having a condenser connected across the same, a mid-tap transformer winding, the opposite sides of said condenser being connected to the respective end terminals of said transformer winding and the mid-tap thereof being connected to the same side of the voltage supply that the heated cathode of the cathode ray tube is connected, and means for reversing the phase of the voltage induced in said transformer winding whereby one or the other of said target portions is illuminated and that when the voltages from said mid-tap to the opposite terminals of the transformer are equal the target portions of said cathode ray tube have equal but minimum energization.

2. A circuit for controlling the selective energization of diametrically opposite portions of the targets in a cathode ray tube, having a control electrode for each portion of the target and a heated cathode, comprising a high ,a twin triode tube, a resistor connected to each plate of the triode tube, the opposite side of each of said resistors being connected together and being adapted for connection to the same side of an alternating current voltage supp-1y source, said twin triode tube having a cathode and a heater therefor, and a control grid for each plate, said cathode being connected to one side of a resistor of relatively high ohmic value, the other side of said resistor being adapted for connection to the other side of said voltage supply, the cathode ray tube having its target conn cted to the supply voltage side of the plate resistors of the twin triode tube, and its control electrodes connected respectively to the plate sides of said triode plate resistors, the heated cathod of said cathode ray tube being connected to the voltage supply side of the heated cathode of the triode tube, the control grids of said triode tube having connected across the same, a mid-tap transformer winding, the mid-tap thereof being connected to the same side of the voltage supply that the heated cathode of the cathode ray tube is connected, and means for reversing the phase of the voltage induced in said transformer winding whereby one or the other of said target portions is illuminated and that when the voltages from said mid-tap to the opposite terminals of the transformer are equal the target portions of said cathode ray tube have equal but minimum energization.

KURT ALBRECHT.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,175,700 Roberts Oct. 10, 1939 2,190,488 Schnoll Feb. 13, 1940 2,219,506 Steimel et al Oct. 29, 1940 2,243,408 Anderson et al May 27, 1941 2,262,407 Rath Nov. 11, 1941 2,263,932 Schnoll Nov. 25, 1941 2,318,140 Clark May 4, 1943 2,366,320 Elston Jan. 2, 1945 2,457,575 Liebscher Dec. 28, 1948 

